Exemplary embodiments of the present invention relate generally to antenna systems. Antenna systems can be used as transmission or reception devices to transmit or receive signals in a system. These systems may be communications, navigation, and surveillance in nature. Signals may be electromagnetic, optical, or acoustic in nature, and the antenna systems may be single element or multi-element in nature. Various types of single antenna elements exist for various purposes to produce radiation characteristics for the system applications.
A single-element GNSS patch antenna is one example of an antenna. At a particular operating frequency, the antenna radiation pattern of a typical single-element Global Navigation Satellite System (GNSS) patch antenna is often fixed based on the type of antenna and supporting ground plane structure. The GNSS generally referees to satellite-based navigation systems such as the Global Positioning System (GPS), GLObal NAvigation Satellite System (GLONASS), the Galileo, BeiDou. (With the theory of antenna reciprocity in mind, it is equitable to discuss the “radiation” characteristics and “reception” characteristics of a given passive antenna as comparable characteristics.) For example, a half-wave patch antenna over a ground plane, will have an antenna pattern with high directivity in the upper hemi-sphere (same side as the patch element), and low directivity in the lower hemi-sphere (i.e., below the ground plane). While these types of antennas perform very well for most GNSS applications, they have limited ability to suppress interference/jamming sources. In addition, single element patch antennas in the known art have limited control of the antenna pattern.
As a result, antenna arrays are common when the performance requirements exceed the capabilities of a single antenna element. These performance requirements may be in terms of directivity, pattern shape, beamwidth, and/or interference suppression, as well as other performance metrics. Antenna arrays use multiple antenna elements that are geometrically distributed to aid in obtaining the performance requirements. Antenna arrays are physically larger than a single-element that is within the antenna array, because an antenna array will be made up of multiple elements. Elements within an antenna array may be provided with amplitude and phase control to control the radiation pattern of the array antenna. Various GNSS array antennas, (i.e., Controlled Reception Pattern Antenna (CRPA)) have been used and researched for GNSS applications of various sizes and capabilities. The calibration of GNSS antenna arrays (i.e., CRPAs) have also been an active area of research where the in situ performance of the antenna array should be considered to ensure satisfactory performance of the as operationally installed antenna array.
GNSS microstrip patch antennas are common due to their low profile, small size, ease of fabrication, and low cost. GNSS patch antennas can be designed in various shapes and configurations to support single and multi-frequencies. Additionally, various types of feeds can be used with patch antennas to connect the antenna element to input/output connection(s). The feed type can be probe fed from below the patch, edge fed, and/or an aperture coupled fed to name a few. Probe feed patch antennas have the advantage that they can be fed from the “backside” of the antenna element and will be addressed in examples of this application. The principles of the present invention may also apply to other feed types.
Microstrip patch antennas can be configured in various shapes with supporting feed locations. While square patch antennas are common and easy to fabricate, circular patch antennas typically provide slightly higher bandwidths. The principles of the present invention may apply to circular patch antennas, square patch antennas, or other shapes of antennas.
The supporting ground plane structure also affects the patch antenna performance. Larger ground planes provide for multipath mitigation (i.e., reduced radiation in the lower hemisphere), while smaller ground planes tend to provide for more of a semi-isotropic radiation pattern. Advanced ground planes have been provided in terms of choke rings. Advanced ground planes materials have also been used in the GNSS community to reduce the radiation in the lower hemisphere.
Other steps have been taken to reduce the multipath and interference from lower elevation angles. One such strategy is to have a circular patch antenna with a hole in the middle, with the hole surrounded by grounding vias. Probe feeds are placed inside the walled off hole. This configuration will increase the minimal elevation angle of the radiation pattern and thus shield it from interfering sources on the horizon. Various reconfigurable antennas have been proposed that add or modify components on the antenna, or change the physical structure of the antenna to modify the operational characteristics of the antenna. For GPS patch antennas, a strategy has been demonstrated to short out the patch using switching diodes, placed on the edges of the patch to attenuate low elevation angle signals. Other techniques have been proposed that use an aircraft body (i.e., ground plane) to nullify undesirable signals below the horizon. There is a need for improved systems and methods to achieve desirable radiation characteristics.
Exemplary embodiments of the present invention may overcome some or all of the shortcomings of the known art. Exemplary embodiments of the present invention deal with the ability to have pattern control using a single element antenna by placing multiple feeds on opposite ends of the antenna element and controlling the amplitude and phase distribution of each of the feed ports. Here, a single element antenna is considered to be a single patch aperture with multiple feeds. Additionally, the amplitude and phase control may include the ability to control the overall gain of each port together, in addition to individually, in a static or automatic sense (i.e., automatic gain control). The amplitude and phase control subsystem may be performed by an amplitude and phase control circuit or performed in software. The feeds on opposite sides of the antenna element may be even in number or odd. The feeds may be combined by a combiner subsystem that may be a circuit or software combiner.
Exemplary embodiments of the invention may control the azimuth pattern by varying the phase of adjacent ports (i.e., ΔγADJ). Exemplary embodiments of the invention may control the elevation pattern by varying the phase of opposite ports (i.e., ΔγOPP). Exemplary embodiments of the invention may control the azimuth and elevation pattern, simultaneously by varying the phase of adjacent ports (i.e., ΔγADJ) and by varying the phase of opposite ports (i.e., ΔγOPP).
Exemplary embodiments of the invention may control the azimuth pattern by varying the amplitude of adjacent ports (i.e., ΔaADJ). Exemplary embodiments of the invention may control the elevation pattern by varying the amplitude of opposite ports (i.e., ΔaOPP). Exemplary embodiments of the invention may control the azimuth and elevation pattern, simultaneously by varying the amplitude of adjacent ports (i.e., ΔaADJ) and by varying the amplitude of opposite ports (i.e., ΔaOPP).
In an exemplary embodiment, the pattern may be controlled in such a way to direct high levels of radiation intensity in a particular direction. The pattern may be controlled in such a way to direct low levels of radiation intensity in a particular direction. Furthermore, the pattern may be controlled in such a way to direct high levels of radiation intensity in a particular direction and direct low levels of radiation intensity in a particular direction, simultaneously.
In one embodiment of this invention, probe feeds are used, whereby the signal is fed from the bottom of the patch element (a conductive patch), placed on top of a dielectric substrate, over a ground plane. Other types of feeds may be used in other exemplary embodiments. In one exemplary embodiment, 4 symmetric feeds (i.e., ports) may be used. For each feed port, the amplitude and phase of each port may be controlled by an amplitude and phase control subsystem (e.g., circuit and/or software). A combiner subsystem (e.g., circuit and/or software) may combine the signals from the ports. The amplitude and phase control subsystem may be part of the antenna system, or may be an integral part of the receiver system. The combiner subsystem may be part of the antenna system or may be an integral part of the receiver system.
In addition to the novel features and advantages mentioned above, other benefits will be readily apparent from the following descriptions of the drawings and exemplary embodiments.